Psocids (barklice, booklice)

Drees, B. M. 2004. Barklice. EEE-0008. Texas Cooperative Extension. College Station, Texas. 3 pp.

Booklice

Psocoptera (the scientific name for this order of insects) are a large group of primitive insects commonly known as booklice, dustlice, deathwatches (Drees and Jackman 1998). Unlike true lice, “booklice” are not external parasites and do not bite man or other animals. The name, “psocid” (short for Psocidae, a family within Psocoptera) may be a better term to use for this group. There are many other psocids that occur outdoors, including barklice species (Drees 2004).

As a group, indoor psocids do little actual damage except when contaminating stored food, but their presence in large numbers can be very annoying. The name, “booklouse”, comes from some species’ association with books, especially in the days before air conditioning, when natural humidity in homes and libraries allowed more frequent growth of mildew on book bindings and pages. Psocids are thought to feed mostly on microscopic molds; however a variety of food items (both plant and animal origin) may be attacked. Indoor inhabiting species of booklice may feed on starched in book bindings, coated papers or wall paper, or the molds growing on starchy surfaces. They may also feed on dried fruits, animal feed, flours, oats and other grains, and cereals, especially if these are stored in damp locations.

Description. The booklouse, such as Liposcelis corrodens Heymons (Psocoptera: Liposcelidae) and similar species such as L. bostrychophila Badonnel commonly found indoors, are very small (1/16 inch or 1 mm long), wingless, and look like small moving whitish to yellowish specks (Fig 1-3). Adults of other less common indoor psocid species, such as the “small-winged southern house psocid”, Psocatropos microps (Enderlein)(Psocoptera: Psyllipsocidae), have wings and actively leap when disturbed (Mockford 1993).

Under magnification, booklice resemble miniature termites with a broad head, narrow mid-section (thorax) and wide abdomen. The first section (femora) of the hind legs is enlarged. All booklice have a bulging clypeus (the upper “lip” area above the mouthparts) and long, filamentous antennae.

Booklice develop from eggs laid singly or in clusters. At optimal temperature and humidity, wingless immature stages or nymphs hatching from eggs develop through 3-4 stages or instars over a period of about 10 days before becoming adults. A complete life cycle, including egg incubation period may average approximately 24 days, although temperature and humidity can affect this life cycle length considerably.

Booklice may become noticeable during warm, moist conditions found in damp rooms, duct work, storerooms, libraries or other favorable habitats that provide food, shelter and proper conditions. They feed mainly on microscopic molds, as well as dead or decayed plant or animal material. Cosmopolitan grain psocids, Lachesilla pedicularia (Linnaeus)(Psocoptera: Lachesillidae), are often found in buildings where cereals, straw products or fresh plant materials are found. The deathwatch psocid, Trogium pulsator Linnaeus)(Psocoptera: Trogilidae), is a winged psocid also found in barns and granaries Borror et al. 1989). These creatures produce a ticking sound by hitting their bodies against paper or similar materials.

Management. Monitor for booklice by visually inspecting areas of infestation. In some cases, particularly if winged species are suspected, glue boards can be placed next to vents or near other suspected habitats to determine the source of infestation. Inspect articles stored in pantries for signs of infestation.

Indoors, management should start with thorough cleaning of infested areas, discarding possible sources of infested food or other materials. Vacuuming susceptible areas has been effective. Increasing light to infested areas suppress dark-living booklice activity. Reducing humidity by opening windows and doors and turning off humidifiers or using fans or dehumidifiers will reduce favorable environmental conditions. Booklice do not survive more than 1-3 weeks if relative humidity is less than 58%.

Plumbing and roof leaks can lead to moist conditions that favor booklice, as can condensation from air conditioning systems. In some cases, such as in loosely constructed buildings, total control of booklice may not be feasible.

Infested articles not discarded can be cleaned and aired or treated to eliminate booklice. Articles (that are resistant to freezing or heat) can be placed in plastic bags and either frozen (kept in freezer at 0°F for 4 days) or heated (30 min at 180°F) sufficiently to kill booklice.

A good listing of insecticides registered for use in these use sites to control booklice is available at: http://edis.ifas.ufl.edu/ig094. Treatment options include aerosol formulations of contact insecticides (acephate, cyfluthrin, lambda-cyhalothrin, pyrethrins with piperonyl butoxide or PBO synergist) applied to cracks and crevices. Some insecticide products that act as fumigants are available to place in storage areas or other small spaces to eliminate pests. For instance, Hot Shot® No-Pest Strip and Vaportape® II, both containing dichlorvos of DDVP, paradichlorobenzene (PDB) crystals or naphthalene cones are sold to prevent pests of insect collections.

Howard Ensign Edwards, author of Life on a Litte-Known Planet E. (P. Dutton and Co., Inc., N.Y. 1966), dedicated his book “…to the booklice and silverfish that share my study with me. May they find it digestible”

Literature cited

Borror, D. J., C. A. Triplehorn, and N. F. Johnson. 1989. An Introduction to the Study of Insects (Sixth Edition). Saunders College Publishing, Ft. Worth. 875 pages.

Drees, B. M. 2004. Barklice. EEE-0008. Texas Cooperative Extension. College Station, Texas. 3 pp.

Drees, B. M., and J. A. Jackman. 1998. A Field Guide to Common Texas Insects. Gulf Publishers, Houston, Texas. 359 pp.

Mockford, E. L. 1993. North American Psocoptera (Insecta). Flora and Fauna Handbook No. 10. Sandhill Crane Press, Inc., Gainesville, FL.

Acknowledgments

The author wishes to thank Drs. Roger E. Gold and Mike Merchant for their review and helpful comments in the development of this fact sheet.

Fig. 1. A book louse, Liposcelis species (Psocoptera: Liposcelidae)(USDA).

Fig. 2. A book louse, Liposcelis species (Psocoptera: Liposcelidae)(photograph by B. M. Drees).

Fig. 3. A book louse, Liposcelis species (Psocoptera: Liposcelidae)(photograph by M. E. Merchant).

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Psocids (barklice, booklice)

Most psocids live outdoors and have wings and are known as barklice.

• They are found on tree bark, leaves of trees and shrubs, and under stones.
• They can become obvious when they assemble in large numbers.
• Barklice feed on fungi, lichen, pollen, decaying plants and other organic material.
• They are harmless to plants and treatment is not needed.

Booklice

Some psocids (usually Liposcelis spp.) are wingless and can be found inside buildings. They are called booklice because they are often found near books or paper.

• Booklice are rarely damaging inside homes and are harmless to people or pets.
• Booklice usually feed on molds, fungi, grains, insect fragments, and other starchy material, including glue from bookbindings.
• In homes, psocids typically are found in damp, warm, undisturbed places where mold and fungi are growing.
  • People commonly find them during summer.
  • They can cause problems if stored cardboard becomes wet.

  In food

  • Psocids are sometimes pests in commercial food storage and food manufacturing facilities.
  • Psocids in food indicate fungal or mold problems.

  How to manage psocids

  Ignore small numbers of psocids. You can choose to physically remove them, including with a vacuum.

  If they are numerous, the most effective method to manage booklice is to reduce moisture. Psocids do not survive when humidity falls below 45% – 50%.

  To reduce humidity:

  • Use a dehumidifier or fan to air out rooms and keep the air moving.
  • Check rooflines for poor attic ventilation, trees overgrowing the roof, and leaf litter in the eaves. Correct any of these conditions.
  • If there is a crawlspace under a home, a pest management company can check to see if there is adequate ventilation and that the crawlspace is dry.
  • Store boxes, bags, books and papers off the floor to minimize exposure to dampness.

  Using pesticides

  Insecticides are normally not necessary. Insecticides are not effective if moisture is still a problem. The products that are typically available to residents are generally not effective against psocids.

  Jeffrey Hahn and Stephen Kells, Extension entomologists